1. Field of the Invention
This invention relates to fiber cords, as used as load carrying members in power transmission belts, and, more particularly, to a method of bonding an ethylene.xcex1-olefin rubber composition to such a fiber cord.
2. Background Art
In response to the demand for energy savings, automobiles have been made increasingly more compact. Engine compartments have likewise been compacted. With engines running at high temperatures, the engine components, including power transmission belts in the engine compartment, are required to perform at high temperatures.
Natural rubber, styrene-butadiene rubber, and chloroprene rubber have been widely used to construct power transmission belts. However, these rubbers tend to crack prematurely in high temperature environments in which they are operated. This cracking is typically a problem in the compression rubber section of the belt.
Research has been carried out to improve the heat resistance of chloroprene rubber to address the problem of premature failure. Alternatives to the above rubbers have been proposed. For example, in Japanese Unexamined Patent Publication No. 6-345948, it is suggested that ethylene-xcex1-olefin elastomers, such as ethylene-propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), and the like, be used for power transmission belts because of the high resistance to heat and cold, and also because these rubbers are relatively inexpensive.
However, ethylene-propylene rubber has a relatively low tear strength, and may have an even lower tear strength in a peroxide vulcanization system. As a result, load carrying cords in the belt may break away during use.
A sulfur vulcanization system generally makes it difficult to achieve a sufficient degree of vulcanization, as a result of which the belt may become excessively worn during operation. This is particularly true of a V-ribbed belt. With this type of belt, wear dust commonly accumulates between ribs, at the base thereof. Eventually, this may cause tack wear which produces problematic noise.
To increase the degree of vulcanization, it is known to use EPDM, with a very large number of double bonds, to alleviate tack wear to a certain extent. However, this may result in a reduction in heat resistance.
There has also been a problem in effectively bonding ethylene-xcex1-olefin elastomer to a fiber cord. It is known to immerse a fiber material in a dipping solution of resorcinol-styrene-butadiene-vinyl pyridine latex, followed by vulcanization-bonding of an EPDM rubber composition to the fiber material. This is disclosed, for example, in Japanese Unexamined Patent Publication No.8-113657. In Japanese Unexamined Patent Publication No.8-113656, a method is disclosed in which fiber material is treated in a bonding solution of resorcinol-formalin-rubber latex after which vulcanization-bonding is carried out with an EPDM rubber composition having a methylene donor, a methylene acceptor, and a silicic compound.
While treatment with a solution of resorcinol-styrene-butadiene-vinyl pyridine latex improves bonding strength, when such fibers are used as load carrying cords in a power transmission belt which is subjected to repetitive flexing, the load carrying cords may prematurely release from the rubber in which they are embedded.
Even when a fiber material is treated with an EPDM rubber composition having a methylene donor, a methylene acceptor, and a silicic compound, such fiber, when used as a load carrying cord in a power transmission belt, that is subjected to repetitive flexing, may also prematurely release from the rubber in which it is embedded.
In one form, the invention is directed to a method of bonding an ethylene.xcex1-olefin rubber composition to a fiber cord. The method includes the steps of: treating a fiber cord with a first treating solution that is at least one of an isocyanate compound and an epoxy compound; after treating the fiber cord with the first treating solution, treating the fiber cord with a second treating solution including resorcinol-formalin-rubber latex; after treating the fiber cord with the second treating solution, treating the fiber cord with a third treating solution including a halogenated polymer and a vulcanizing agent; and after treating the fiber cord with the third treating solution, vulcanization-bonding an unvulcanized ethylene.xcex1-olefin rubber composition to the fiber cord.
The third treating solution may include a bonding rubber.
The halogenated polymer and bonding rubber in the third treating solution may be present in a ratio of 3:7 to 7:3.
In one form, the fiber cord has a solid pickup of a bonding agent in the range of 3-16% by weight at the completion of bonding, with the bonding agent made up of the halogenated polymer in the third treating solution.
The bonding rubber may be an ethylene.xcex1-olefin rubber.
In one form, the ethylene.xcex1-olefin rubber is at least one of a) EPDM rubber derivable from an ethylene-propylene-diene monomer and b) EPR rubber.
The cord may be a cord of twisted fiber that is at least one of aramid fiber and polyester fiber.
The isocyanate compound may be at least one of 4,4xe2x80x2-diphenylmethane diisocyanate, tolylene 2,4-diisocyanate, polymethylene polyphenyl diisocyanate, hexamethylene diisocyanate, polyaryl polyisocyanate, and the like.
The isocyanate compound may be mixed with at least one of an organic solvent and an organic solvent that is at least one of toluene and methyl ethyl ketone.
The method may further include the step of reacting the isocyanate compound with a blocking agent to produce a polyisocyanate with a blocked isocyanate group.
The epoxy compound may be at least one of a) a polyhydric alcohol, b) a product obtained by the reaction of a polyalkylene glycol with a halogen-containing epoxy compound, and c) a product obtained by the reaction of a polyhydric phenol with a halogen-containing epoxy compound.
The step of treating the fiber with a first treating solution may involve immersing the fiber cord in the first treating solution for 0.5-30 seconds and then drying the fiber cord for 2-5 minutes at 150-190xc2x0 C.
The resorcinol-formalin-rubber latex of the second solution may be a mixture of a resorcinol-formalin polycondensate and a rubber latex, with the resorcinol to formalin molar ratio being in the range of 3:1 to 1:3.
The rubber latex may be at least one of an acrylonitrile-butadiene rubber latex (NBR latex) and a hydrogenated acrylonitrile-butadiene rubber latex (H-NBR latex).
The resorcinol-formalin polycondensate may have a resin content of 5-100 parts by weight per 100 parts by weight of rubber latex, with the total solid content of the resorcinol-formalin-polycondensate being between 5-40%.
The step of treating the cord with the second treating solution may involve immersing the fiber cord in the second treating solution at a temperature of 5-40xc2x0 C. for 0.5-30 seconds, and then drying the fiber cord for 1-3 minutes at 200-250xc2x0 C.
The halogenated polymer of the third treating solution may be at least one of chlorinated rubber, chloroprene rubber, and chlorosulfonated polyethylene rubber.
The bonding rubber may be at least one of ethylene.xcex1-olefin rubber, NBR, SBR, and ethylene.xcex1-olefin rubber that is at least one of EPDM and EPT.
The vulcanizing agent may be at least one of dibenzothiazil disulfide (MBTS), tetramethylthiuram disulfide (TMTD), N-cyclohexyl-2-benzothiazil sulfenamide (CBS), tetramethylthiuram monosulfide (TMTM), mercapto-benzothiazole (MBT), PZ (ZnMDC), and sulfur.
The invention is further directed to a method of bonding an ethylene.xcex1-olefin rubber composition to a fiber cord. The method includes the steps of: treating a fiber cord with a first treating solution including at least one of an isocyanate compound and an epoxy compound; after treating the fiber cord with the first treating solution, treating the fiber cord with a second treating solution including resorcinol-formalin-rubber latex, with the rubber latex including at least an acrylonitrile-butadiene rubber latex; after treating the fiber cord with the second treating solution, treating the fiber cord with a third treating solution including a chlorinated rubber, an ethylene.xcex1-olefin rubber, and a vulcanizing agent, with the ratio of chlorinated rubber to ethylene.xcex1-olefin rubber being 3:7 to 7:3, and so that the fiber cord has a solid pickup of a bonding agent in the range of 3-16% by weight at the completion of bonding, with the bonding agent including rubber contained in the third treating solution; and after treating the fiber cord with the third treating solution, vulcanization-bonding an unvulcanized ethylene.xcex1-olefin rubber composition to the fiber cord.
The invention is further directed to a fiber cord-rubber laminate made according to the process described above.